The J, K and N Class ships were developed as a result of the Admiralty under pressure to cut costs but requiring more new and powerful destroyers. The cost of further Tribal Class ships was attractive but could not be justified on cost grounds. The Staff requirement also required a return to a heavy torpedo outfit. While some see these ships as cut down versions of the Tribal Class they were the first to see the introduction on Longitudinal Frames and other weight saving methods of construction. Several ships owed this method of construction to their survival, HMS Javelin was mined and reduced to less than half her original length, but she was towed in and repaired.

Many of the J and K Classes served and were lost in the Mediterranean they participated in many successful engagements, accounting for Italian cruisers, destroyers and many merchant ships.

Pennant numbers changes from F .. to G .. in late 1940 (in or around December).